A bicycle generally has a frame. Whatever the form of cycling planned or whoever may be the user, frames have a substantially similar geometry. This geometry is characterized by the presence of a first rod, a second rod, and a third rod associated with a hinge, the assembly forming a support structure. The three rods as well as the hinge are such that their axes of development are situated in a same plane called the plane of the frame. The rods and the hinge are joined in sets of two. Furthermore, a frame of this kind has a rear wheel support structure. The rear wheel support structure is mounted on the second rod at two different places.
Two elements are mounted on said frame. More particularly, a saddle, a handlebar associated with a front fork and a front wheel, a rear wheel and a crankset. The crankset and rear wheel are rotationally integral with each other, at least in one sense of rotation. To this end, the crankset and the rear wheel are connected by a chain.
The different morphologies of users in the different types of cycling practices make it necessary to have a wide range of frames. Indeed, the user's position on a bicycle is not the same depending on the different practices used since the needs in terms of physical performance, aerodynamic qualities and user comfort are not the same. Present-day bicycles have many elements whose characteristics vary from one bicycle to another depending on the form of cycling planned.
For example, the geometry of a frame specially designed for the triathlon is such that it fosters comfort and efficiency when the user is riding with aerobars. This means especially that there is a shaft between the saddle and the crankset as well as rods associated with the hinge that are relatively short compared with a frame designed for peloton racing. This geometry is aimed at giving the user a more forward position so that the user can use the aerobars more comfortably and at facilitating the muscular transition from cycling to running during a triathlon. This geometry makes the bicycle very unwieldy and hence dangerous to use in peloton conditions or in bends taken at high speeds.
Top-of-the-range bicycles designed for road competition are very rigid so to provide maximum efficiency. This extreme rigidity is often obtained to the detriment of comfort. These top-of-the-range bicycles are thus not comfortable for long-distance use and for use on roads whose surfaces are not perfectly smooth. The many jolts suffered by the cyclist and their intensity also cause considerable additional muscle fatigue. Furthermore, the bicycle keeps bouncing off the uneven features on the road, the wheels lose contact with the road and this causes a loss of traction and hence the loss of part of the energy provided by the cyclist while pedaling.
The frames are thus classified in categories such as for example against-the-clock (or “time trial”) frames, road-race frames, training frames, or again triathlon frames. However, their geometry is suited to only one type of cycling whereas many users do not restrict themselves to only one form. The users therefore have to choose between several frames, one for each form, or have only one frame suited to only one form but which they must also use for the others even when they are adapted thereto. This therefore entails costs in equipment or costs in terms of performance, comfort and safety.
The fact that different geometries are needed to adapt to the needs of a maximum range of morphologies of users and a maximum range of forms of cycling also gives rise to drawbacks for frame manufacturers. Most bicycle frame manufacturers, and especially manufacturers of carbon frames, find it impossible to manufacture numerous sizes and geometries of frames because of the costs entailed. The manufacturers of carbon frames therefore tend to propose a limited number of different frame sizes. This limits the number of users who can use their frames. A proportion of the users having body member shapes less common than other users, for example users smaller then the majority of cyclists or users for whom the ratio between torso length and leg length is greater or smaller than that of the majority of the cyclists. These users therefore can not find top-of-the-range carbon frames with a size corresponding to their body member shape.
Italian patent TV94A000114 describes a bicycle frame device comprising a main shell or housing for the crankset in which a detachable body member is mounted. The detachable body member comprises a special housing that can be horizontally off-centered. The crankset is mounted in the special housing. Thus, depending on the detachable body member introduced into the main housing and more particularly depending on the position of the special housing in said detachable body member, the crankset can be situated horizontally at different positions on the frame relative to the saddle.
However, a horizontal shift of this kind, while it enables the angle of the axis defined by the position of the saddle and of the crankset to be adjusted, cannot easily be adapted to all body member shapes of users because there are few possibilities of positioning the crankset. Furthermore, it is still difficult to define a position that is made to measure for every user, for it is difficult to adapt both the value of the distance between the saddle and the crankset and the angle of the axis between the crankset and the saddle. Similarly, a device of this kind in no way modifies the rigidity of a frame of this kind.
Swiss patent CH-A-260 468 and U.S. Pat. No. 4,808,147 each describe a bottom bracket assembly comprising a circular-based cylinder (detachable body member) provided with a special housing designed to receive the pedal, the special housing being off-centered relative to the axis of the detachable body member. The detachable body member is axially blocked in the bracket assembly casing. It is possible to adjust the angular position of the special housing.
The drawback of the solutions proposed by the '468 Swiss patent and the '147 U.S. patent is that the cylinders are blocked only axially in the bracket assembly casing. Under the pressure communicated by the pedaling, it is possible that the detachable body member, owing to its circular-based cylindrical shape, will shift rotationally in its support. The position of the special housing is thereby modified. This is a major drawback since the purpose of these inventions is precisely to achieve the setting that results from the position of the special housing.
These devices therefore do not enable the efficient adapting of one bicycle to several users or several forms of cycling.